Class I molecules are able to present antigens from opportunistic microorganisms to CD8 T cells. In this grant we will dissect the role of class IB antigens in this process. This includes determining how IB molecules present ligands recognized by alpha-beta as well as gamma-delta T cells, identifying the peptides that IB molecules present, and defining peptide motifs for several class IB alleles. We will extend our knowledge of class IB genes/antigens by characterizing newly identified genes in the Q, T, and M regions of the murine MHC. The role of Tap molecules in antigen presentation will be investigated by assessing what effect polymorphisms in human Tap genes have on their function. Together, this grant will integrate the structure/function of class IB molecules in the presentation of ligands derived from infectious organisms responsible for disease in immunocompromised individuals as well as determine how Tap molecules function in antigen presentation.